The present invention relates to a process for producing an electrophotographic photoreceptor using an optically functional coating solution, an electrophotographic photoreceptor and an image-forming apparatus.
In recent years, optically functional organic materials have attracted much interest in electrophotographic photoreceptors, organic electroluminescence elements, memory elements and wavelength conversion elements in view of the productivity, the ease of material designing and the safety. They have been put to practical use upon making various improvements. From the aspects of stabilization of organic electronic devices and prolongation of their life, for example, materials that do not cause the change in morphology of films owing to Joule heat generated have been required for organic electroluminescence elements. Further, materials having not only a chemical stability to ozone or NOx but also a stability to physical stresses such as heat and mechanical forces have been required for electrophotographic photoreceptors. For example, an electrophotographic photoreceptor has been described in detail.
With respect to an electrophotographic photoreceptor, a so-called functionally separated (laminated) structure in which a charge-generating layer and a charge transfer layer are separated has been designed in view of a photoreceptivity and a stability, and it has been put to practical use. The electrophotographic photoreceptor of this structure has two layers, a layer to which a charge-generating material is adhered with an appropriate resin as a binder and a layer obtained by dispersing or dissolving a charge transfer material thereon in a binder resin. The layer containing the charge transfer material contains a hole transfer material in many cases. A thermoplastic resin such as a polycarbonate resin, a polyester resin, an acrylic resin or a polystyrene resin and a thermosetting resin such as a polyurethane resin or an epoxy resin have been studied as the binder. In this case, the surface of the charge transfer layer has to be negatively charged by corona charge or biased-roller charge. There are problems that photoreceptor characteristics are decreased from various causes such as deterioration of a resin with ozone generated at this time, wear by electric shock due to discharge in the surface of the photoreceptor, decrease in photoreceptivity, decrease in chargeability and a mechanical destruction due to abrasion in the subsequent toner development, transfer onto paper and cleaning.
Various studies have been made to cope with these problems. For example, a polysiloxane resin is used as a copolymerizable component or blended with another resin. Specific examples thereof include the use of a thermosetting resin containing a polysiloxane resin in a charge transfer layer (Japanese Patent Laid-Open No. 238062/1986), a protecting layer containing a polysiloxane resin (Japanese Patent Laid-Open No. 108260/1987), a protecting layer obtained by dispersing a thermosetting polysiloxane resin in silica gel, a urethane resin or a fluororesin (Japanese Patent Laid-Open No. 346356/1992), and the use of a resin obtained by dispersing a thermosetting polysiloxane resin in a thermoplastic resin as a binder resin of a protecting layer or a charge transfer material (Japanese Patent Laid-Open No. 273252/1992). The increase in performance, the prolongation of life and the improvement of the cleaning property on the photoreceptor have been studied upon using characteristics of the polysiloxane.
Although the polysiloxane has characteristics that are not found in other resins, such as a transparency, a resistance to insulation breakdown, a light stability and a low surface energy, a compatibility with organic compounds is extremely poor. For this reason, it has not been singly used as a resin constituting a charge transfer material, but has been used for improving a resin constituting a charge transfer material through copolymerization or blending. For the polysiloxane resin alone to be used as a binder constituting a charge transfer layer, there is a need to find a charge transfer material soluble in a polysiloxane resin. To this end, various studies have been made. Examples thereof include the use of a resin in which a charge transfer agent having an unsaturated bond is directly bound to a polysiloxane such as poly(hydrogenmethylsiloxane) through hydrosilylation as a binder resin of a protecting layer or a charge transfer material (Japanese Patent Laid-Open No. 319353/1996), the use of an inorganic thin film formed by plasma CVD as a protecting layer (Japanese Patent Laid-Open No. 333881/1995), the use of a thin film formed by the sol-gel method as a protecting layer (Proceedings of IS and T""s Eleventh International Congress on Advances in Non-Impact Printing Technologies, pp. 57 to 59(1995)), and the use of an organosilicon-modified hole-transferring compound in which silicon having a hydrolyzable group is directly introduced in a charge transfer agent as an electrophotographic photoreceptor (Japanese Patent Laid-Open No. 190004/1997). Of these, the products disclosed in Proceedings of IS and T""s Eleventh International Congress on Advances in Non-Impact Printing Technologies, pp. 57 to 59, U.S. Pat. No.2,575,536 and Japanese Patent Laid-Open No. 190004/1997 have drawn high attention because the siloxane forms a three-dimensional network to give a strong film whereby mechanical strengths are greatly improved.
Nevertheless, in Proceedings of IS and T""s Eleventh International Congress on Advances in Non-Impact Printing Technologies, pp. 57 to 59, a specific structure of a compound used is not described at all. Further, Japanese Patent Laid-Open No. 190004/1997 discloses a method in which an unsaturated aliphatic group bound or newly bound to an aromatic group constituting an organosilicon-modified hole-transferring compound and a silane having hydrogen and a hydrolyzable group as a substituent of a silicon atom are linked by a hydrosilylation reaction in the presence of a catalyst made of a platinum compound. However, in this reaction, an isomer different in a bonding position of silicon is formed, and a reductant in which an unsaturated aliphatic group is reduced is easily formed. Thus, as is clear from a spectrum of Japanese Patent Laid-Open No. 190004/1997, a mixture of plural compounds tends to be provided. When this reductant is used as a charge transfer layer, no siloxane linkage is formed, and strengths of a film are decreased. Further, when column chromatography is conducted for purification of this, the yield is notably reduced owing to the decomposition and the reaction of the organosilicon-modified hole-transferring compound. Moreover, U.S. Pat. No. 2575536 discloses specific compounds. It is, however, generally known that characteristics of an electrophotographic photoreceptor are greatly influenced by a molecular structure such as a basic skeleton of compounds used or a polarity of a bonding chain, and the compounds disclosed are still unsatisfactory.
Meanwhile, electron-transferring materials have been assiduously studied in the field of electrophotographic photoreceptors. For example, trinitrofluorenone described in Japanese Patent Publication No. 10496/1975, dicyanomethylenefluorenone derivatives described in Japanese Patent Laid-Open No. 143764/1986, anthraquinone derivatives described in Japanese Patent Laid-Open No. 225151/1986, thiopyrane derivatives described in Japanese Patent Laid-Open No. 222477/1985, fluorenone derivatives described in Japanese Patent Laid-Open Nos. 279582/1993, 233134/1995 and 258189/1995, benzotiazole or benzoxazole derivatives described in Japanese Patent Laid-Open Nos. 245601/1996, 283249/1996, 301858/1996 and 286402/1996, benzoquinone derivatives described in Japanese Patent Laid-Open No. 15878/1996, diphenoquinone derivatives described in Denshishashin Gakkaishi, vol. 30, No. 3, 266 (1991), imide compound derivatives described in Japanese Patent Laid-Open Nos. 25136/1993, 25174/1993, 117274/1993, 125043/1993 and 132464/1993, and an electron-transferring polymer obtained by introducing an electron-transferring group into a polymer as described in Japanese Patent Laid-Open Nos. 12153/1977 and 12154/1977 and Macromolecules, 22, 2266 (1989) are disclosed. However, the main aim of these materials is to improve a low solubility in an organic solvent or a low compatibility with a binder polymer that is a substantial defect of an electron-transferring material.
Further, in an electrophotographic photoreceptor, an undercoat layer or an intermediate layer is generally interposed to improve an adhesion between a photoreceptive layer and a substrate and a coatability of a photoreceptive layer, to protect a surface of a substrate, to cover a defect of a substrate, to protect a photoreceptive layer from electrical breakdown and to improve a carrier injecting property of a photoreceptive layer.
In case of a positively charged electrophotographic photoreceptor, an electron-generating material is generally used in an uppermost surface layer. Especially in case of a positively charged electrophotographic photoreceptor in which a charge-generating layer is formed on a hole-transferring charge transfer layer, a surface-protecting layer is formed to offset low mechanical strengths of a charge-generating layer.
In the undercoat layer or the surface-protecting layer of the positively charged electrophotographic photoreceptor, it is advisable to basically use an electron-transferring material. For example, Japanese Patent Publication No. 35551/1986 and Japanese Patent Laid-Open No. 160147/1984 describe that an undercoat layer contains an electron-accepting material.
When an electron-transferring material is used for this purpose in, for example, an undercoat layer, this material is dissolved in a coating solvent when forming the undercoat layer. When a photoreceptive layer is further formed on the undercoat layer through coating, the material has to be insoluble in the coating solvent of an upper layer.
However, it is difficult to attain the same with this material. There are problems that the electron-transferring material is dissolved in coating of the upper layer to cause delamination or cracking of the undercoat layer and no satisfactory electron transferability can be retained owing to dissolution.
Further, when the electron-transferring material is used as a surface-protecting layer, it is advisable that a film is as thin as possible for retaining electrical characteristics. However, no satisfactory strengths are obtained with the material dispersed in a binder polymer, and it is impossible to reduce a thickness of a film. Accordingly, there are problems that a residual potential is generated and a surface potential is increased in cycles.
Further, in order to improve this, Japanese Patent Publication No. 86694/1995 discloses that a condensed layer of an alkoxysilane compound having an electron-accepting atom or an electron attractive group is used in a surface-protecting layer. The surface-protecting layer obtained by this method is excellent in strengths, but has a low electron transferability. Thus, it still suffers problems that a residual potential is generated and a surface potential is increased in cycles.
For solving these problems, we developed novel materials disclosed in Japanese Patent Laid-Open No. 95787/1998, and indicated that these materials have excellent characteristics.
It was, however, found that even though using an optically functional organosilicon compound, like these materials, in which silicon having a hydrolyzable group is directly introduced to allow hybridization of organic and inorganic materials through chemical bonding, phase separation occurs before a curing reaction only by mixing and coating the same in the formation of a cured film so that a uniform film is not obtained in many cases.
Accordingly, as disclosed in, for example, U. S. Pat. No. 5,116,703 and Japanese Patent Laid-Open No. 188764/1997, a method is used in which organic material and inorganic material precursors are previously co-hydrolyzed and partially reacted and the resulting product is then coated. The co-hydrolysis is conducted by dissolving these materials in a soluble solvent, adding an appropriate amount of water, and adding an acid catalyst such as acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid or a transesterification catalyst such as alkoxides of various metals. This method is quite effective for obtaining a uniform film.
Nevertheless, these catalysts activate not only the hydrolysis but also a crosslinking reaction after the hydrolysis, and the reaction proceeds even at room temperature. Thus, gelation occurs, and a so-called pot life is short.
For solving this point, U.S. Pat. No. 2,721,106 indicates a method in which co-hydrolysis is conducted using a catalyst insoluble in a system and a polysiloxane is separated from the system after formation. In comparison with the use of an ordinary liquid catalyst as a uniform solution by being dissolved in a system, the reaction rate in this method is low, and the reaction proceeds only on the surface of the catalyst. Therefore, it is generally used by heating.
Accordingly, unless a material similar in reactivity and compatibility is used, only the reaction of a highly reactive material might proceed to cause phase separation or crosslinking. U.S. Pat. No. 2,721,106 discloses only a material which contains an organic component with a low molecular weight and which can easily form a relatively uniform hybrid film of organic and inorganic components. It does not disclose a material effectively used in a material system in which an organic component has a molecular weight of more than 200, more than 300 or more than 400 and is greatly different in properties from an inorganic component. Thus, the development of a process for producing an electrophotographic photoreceptor upon using excellent characteristics of a material as disclosed in Japanese Patent Application Nos. 351809/1997 and 187931/1996 and Japanese Patent Laid-Open No. 95787/1998 has been in demand.
The present invention provides a process for producing an electrophotographic photoreceptor in which an electrophotographic photoreceptor excellent in photoelectric characteristics and mechanical strengths and having a long life can stably be obtained on an industrial scale over a long period of time using a stable coating solution having a long pot life.
The present invention also provides an electrophotographic photoreceptor excellent in stability, photoelectric characteristics and mechanical strengths and having a long life.
The present invention yet provides an image-forming apparatus excellent in stability and having a long life.
The first aspect of the present invention is a process for producing an electrophotographic photoreceptor, which includes contacting a solution containing at least one of optically functional organosilicon compounds represented by formula (I)
Fxe2x80x94[Dxe2x80x94A]bxe2x80x83xe2x80x83(I)
wherein
F represents an organic group derived from optically functional compounds,
D represents a flexible subunit,
A represents a substituted silicon group having a hydrolyzable group represented by xe2x80x94Si(R1)(3xe2x88x92a)Qa in which R1 represents hydrogen, an alkyl group or a substituted or unsubstituted aryl group, Q represents a hydrolyzable group, and a represents an integer of 1 to 3, and
b represents an integer of 1 to 4
with a solid catalyst for reaction, then separating the solid catalyst to form an optically functional coating solution, and coating and curing the optically functional coating solution to form a layer made of a cured film.
The organic group F derived from the optically functional compounds may be a hole-transportable group or an electron-transportable group.
The organic group F derived from the optically functional compounds may be a group represented by formula (II), (III-1) or (III-2) 
wherein
Ar1 to Ar4, independently from each other, represent a substituted or unsubstituted aryl group,
Ar5 represents a substituted or unsubstituted aryl or arylene group, provided at least one to four of Ar1 to Ar5 have a binding site capable of being bound to a bonding group represented by xe2x80x94Dxe2x80x94A in formula (I), and
k represents 0or 1. 
wherein
R2 to R5, independently from each other, represent hydrogen, a halogen, a nitro group or a cyano group,
Z1 and Z2, independently from each other, represent xe2x95x90), xe2x95x90C(CN)2, xe2x95x90C(CO2Ra), xe2x95x90Nxe2x80x94CN or xe2x95x90Nxe2x80x94Ara in which Ra represents an alkyl group having 1 to 10 carbon atoms or a substituted or unsubstituted aryl group having 1 to 10 carbon atoms, and Ara represents a substituted or unsubstituted aryl group, and
o to r, independently from each other, represent 0, 1 or 2.
In the aforementioned process, at least one of the compounds having the group capable of being bound to the optically functional organosilicon compounds represented by formula (I) may be added to the optically functional coating solution before being contacted with the solid catalyst for reaction.
Also, at least one of the compounds having the group capable of being bound to the optically functional organosilicon compounds represented by formula (I) may be added to the optically functional coating solution after separating the solid catalyst.
In the aforementioned process, at least one curing catalyst may be added to the optically functional coating solution.
The second aspect of the present invention is an electrophotographic photoreceptor having at least one layer made of the cured film formed by the aforementioned process for producing the electrophotographic photoreceptor.
The layer made of the cured film may be the uppermost surface layer.
The third aspect of the present invention is an image-forming apparatus having at least an electrophotographic photoreceptor and its charging unit, the electrophotographic photoreceptor being the aforementioned electrophotographic photoreceptor.
The charging unit may be a contact-type charging system such as biased roller type charging system.
According to the process for producing the electrophotographic photoreceptor in the invention, the coating solution having the long pot life and the improved stability is used upon separating the solid catalyst, whereby the electrophotographic photoreceptor can stably be produced on an industrial scale over a long period of time. Further, the use of the optically functional organosilicon compounds represented by formula (I) makes it possible to form the siloxane-type crosslinked cured film and produce the electrophotographic photoreceptor having high photoelectric characteristics and also strong mechanical strengths.
In the electrophotographic photoreceptor of the invention, the coating solution having the long pot life and the improved stability is used upon separating the solid catalyst, and the optically functional organosilicon compounds represented by formula (I) are used, with the result that the siloxane-type crosslinked cured film can be formed and high mechanical strengths are realized while having the excellent stability and the high photoelectric characteristics.
The image-forming apparatus of the invention is excellent in stability and has a long life because the electrophotographic photoreceptor of the invention is mounted thereon.